Trench drain gates will prevent large debris from entering the drainage system, and will also prevent flooding with high water levels. They are an indispensable component to any drainage system. There are several types of grates, and repairing these will require different tools and knowledge.
Most newer trench drain gates use a locking system that won't require you to tear apart the concrete or break the grate to remove it. With these there is typically a small lever that runs along the inside of the grate. At the end of the grate system is a small bar that is flush with the grate. You will need to use a flathead screwdriver to pull the bar so the L shape is facing up, and then pull back on the bar to release the lock. This will allow you to remove the section that is damaged and simply replace the single section.
Wood grates aren't used as often now since they don't resist weathering as well. Some older applications may still use these. Wood grates are also the easiest to work with. You simply need to remove the grate, cut out the damaged section, and replace it with new wood pieces. You can then seal the wood to offer more weather resistance.
Cast Iron Grates
Cast iron trench drain grates are very common. They look nice and will last for decades, if not longer. The problem is removing them. If you need to repair a damaged cast iron grate, you will need to break off the fins or flanges that hold the grate in place. In doing this, you are essentially ruining the grate and will need to replace the whole thing. If you have a section of cast iron that is just scratched or gouged, you can typically correct this without removing the entire grate. You can purchase paint products that are made just for cast iron that will fill in the damaged area, creating a smooth surface again.
Grates in Concrete
This isn't as common in residential applications, but some communities do use this type of grate. Repairing these may require you to chip away at the concrete surrounding the grate to remove it. This will also require that you pour new concrete in the area to place the new grate.
Flip Top Grates
Many people are choosing these types of grates for the ease of use. These will be installed in concrete, but have a top that lifts off the grate. To lift the top you simply need to put on a pair of gloves and find the release lever under one of the slats in the grate. Activate the lever and pull up on the top. As long as the framework for the grate isn't damaged, you can simply remove the screws and hinges, make the necessary repairs, and reinstall the top portion of the grate. These are more expensive to install, but will last a lifetime since working on them is much simpler.